Ductile cobalt strip



March 17, 1970 A. T. CAPE 3,501,277

DUCTILE COBALT STRIP Original Filed March 11, 1966 3,501,277 DUCTILE COBALT STRiP Arthur T. Cape, Montcrey, Calif., assignor to Coast Metals, Inc., Little Ferry, N1, a corporation of Delaware Original application Mar. 11, 1966, Ser. No. 533,423, new Patent No. 3,425,828, dated Feb. 4, 1969. Divided and this application Jan. 13, 1969, Ser. No. 790,888

Int. Cl. 1322f 7/00; C22c 19/00 U.S. Cl. 29-182 2 Claims ABSTRACT OF THE DISCLOSURE A ductile cobalt strip or the like is formed from a cold-formable mechanical mixture consisting of cobalt powder and iron powder, the iron powder forming from about 2% to about 4% by weight of the mixture. The cobalt has an hexagonal close-packed crystal structure.

This application is a division of my copending application, Ser. No. 533,423, filed Mar. 11, 1966, and allowed July 25, 1968, now Patent No. 3,425,828.

The invention relates to a ductile cobalt strip or the like, produced from a mechanical mixture consisting of cobalt powder and a small amount of iron powder.

It has heretofore been proposed, as in the Faulkner Patent No. 3,091,022, to provide a cold-formable predominantly cobalt alloy by changing the crystalline structure of the cobalt, which, at room temperature, has an hexagonal close-packed crystall structure, to a face-centered cubic crystalline structure. This is accomplished by incorporating in or adding to the cobalt at least one of the elements carbon, iron and nickel, in a predetermined amount. Although commercially available cobalt may contain a small amount of nickel, iron, carbon or other impurities which cannot be avoided during refinement of the metal, these metals or elements are not present in sutficient amounts nor in the proper proportions required to retain a face-centered cubic structure at room temperature.

The predominantly cobalt alloy in the aforesaid Faulkner patent is made by melting under standard furnacing procedures, preferably by vacuum melting, and the alloy may then be hot-Worked, or may be cold-worked by wellknown methods to produce sheet, tubing, wire, strip, etc.

It has also been proposed, as described in an article entitled Properties and Applications of Cobalt Strip by Fraser, Evans and Mackiw, on pages 80-84 of the July 1964 issue of Metal Progress, to produce ductile cobalt strip by compacting cobalt powder of high purity (99.92%). The powder is rolled into a continuous coil of green strip which is then sintered and hot rolled, and the densified cobalt strip is cold-rolled to the desired gauge or thickness. The hot rolling is performed at 1750 F. In the cold rolling, the strip is cold rolled to nearly the density of solid cobalt and finally, it is annealed in bell furnaces at temperatures up to 1700 F. for 1 hour. The finished cobalt strip consists of combined hexagonal closepacked and face'centered cubic structures, the mixture of these depending on the actual annealing temperature.

I have found that I can produce a cold-formable predominantly cobalt product without changing the hexagonal close-packed crystal structure of the cobalt, and with a minimum of annealing of the cold-formed product by utilizing, to form the product, a mechanical mixture of cobalt powder and iron powder, with the iron powder comprising from about 2% to about 4% by weight of the mixture.

In general, the powders in the mixture should be of a size' of minus 150 mesh, but preferably not smaller than 500 mesh.

3,501,277 Patented Mar. 17, 1970 The mixture of powders is compacted by cold pressure or by cold rolling into a fiat plate or sheet, or into a continuous coil, which is then sintered, if necessary, to agglomerate the particles of powder into a workable mass.

After sintering, the cold pressing or cold-rolling is continued until strip or foil of the desired gauge or thickness is obtained.

The inclusion of the iron powder in the mixture permits compacting with a minimum of annealing, but hot rolling may be used to increase the readiness with which the strip is reduced to smaller gauges.

The strip or foil may be used as such, or may be formed into tubing, wire, etc.

The maximum etfect, for the purposes of this invention, is obtained by using from about 3% to about 3 /2 by Weight of iron powder in the mixture.

Studies using X-ray diffraction show that the structure of both the sintered material as well as the finished strip or coil is overwhelmingly hexagonal close-packed, and no evidence of a face-centered cubic structure has been found.

Microscopic examination establishes that there is little or no solid solution of the iron in the cobalt, and that in the finished strip or foil, the iron is found in long stringers and not in solid solution in the crystals of Cobalt. The structure of the finished strip, as it appears at a magnification of 270x, is shown in the acompanying drawing, wherein the stringers of iron, in the matrix of cobalt, having an hexagonal close-packed crystal structure, are readily seen as lines of iron rich segregation. The formation of a face-centered cubic crystalline structure, such as is found in the product of the :Faulkner patent and in the product of the Metal Progress article referred to above, requires the solid solubility of the iron in the cobalt in Faulkners invention, or repeated annealing of the cobalt strip in the Metal Progress method.

I have thus produced a cobalt strip or foil by a coldforming method, which strip or foil is characterized by the essentially hexagonal close-packed crystal structure of the cobalt, and by the presence of a small amount of iron in the form of long stringers, and substantially none of which is in solid solution in the cobalt.

Having thus described my invention, I claim:

1. A cold-formed strip or foil consisting of a mechanical mixture of cobalt and from about 2% to about 4% by Weight of iron, said strip or foil having essentially all of its cobalt of an hexagonal close-packed crystalline structure, and its iron in the form of stringers distributed throughout the cobalt, with substantially none of the iron in solid solution in the cobalt.

2. A cold-formed strip or foil consisting of a mechanical mixture of cobalt and from about 3% to about 3.5% by Weight of iron, said strip or foil having essentially all of its cobalt of an hexagonal close-packed crystalline structure, and its iron in the form of stringers distributed throughout the cobalt, with substantially none of the iron in solid solution in the cobalt.

References Cited UNITED STATES PATENTS 3,091,022 5/1963 Faulkner 29191.2 3,270,409 9/1966 Grant 226 3,330,654 7/1967 Sweet 75214 3,337,337 8/1967 \Veeton 75-206 XR 3,396,015 8/1968 LaPlante 752l4 3,445,624 5/1969 Sunnen 75170 XR BENJAMIN R. PADGETI, Primary Examiner A. I. STEl'NER, Assistant Examiner US Cl. X.R. 

